Blue Damselfly ID

A work in progress.

The identification of blue damselflies is often difficult for newcomers to dragonflies. Here I will attempt to show the key features for identifying the blue damselflies that occur in Hampshire - Southern, Azure, Variable and Common Blue damselflies. (It is likely that Variable is extinct in Hampshire but I search in hope). Unless we have a re-colonisation of Dainty Damselfly the males are the only predominantly blue and black damselflies occurring in England. These damselflies are a little over an inch in length so close focusing binoculars are essential to be able to pick out the key features.

You will read in field-guides that Southern may occupy the same streams as Azure but seldom the same areas. At both the Ober Water and Latchmore Brook in 2010 I saw Southern, Azure and Common Blue within 20m of one another (3 Southern and 1 Azure male within a foot of one another!) .

If you click on the images below a larger image will open in a new window which you can saved to your computer.

Male blue damselflies

The key features in separating the male blue damselflies (other than the definitive pronotum which may be difficult to see/photograph from some angles) are Segments 2, 8 and 9 (S2, S8, S9) and the presence/absence of the 'Coenagrion spur' - see the side on picture a little lower down. Please note that any phrases here should be prefixed with "usually"!

Male Common Blue Damselflies have broad blue antehumeral (shoulder) stripes; a mushroom or club shaped mark on S2; S8 and S9 are completely blue apart from two tiny black spots on S9; in side view (see below) it lacks the Coenagrion spur of the other blues.

Male Southern Damselflies have narrower antehumerals than Common Blue; a 'mercury' mark on S2; S8 is all blue and the top 1/2 of S9 is blue; S3-S5 have spear shaped black marks; in side view the Coenagrion spur is obvious.

Male Azure Damselflies also have narrower antehumerals than Common Blue; S2 has a 'Whisky tumbler' or U-shaped mark; S8 is all blue and S9 is about 2/3 blue with a black 'bow-tie' at the base; the Coenagrion spur shows when viewed from the side.

Male Variable Damselflies usually have broken or reduced antehumerals; S2 has a 'wine goblet' mark; S8 is blue with two black spots while S9 is more than 1/2 black; as for Azure and Southern, the Coenagrion spur shows when viewed from the side. If in doubt, and you can get a good view, the pronotum is strongly tri-lobed and is diagnostic. You can get an idea from this picture below - both Southern and Azure show a much clearer pale line at the rear edge of the pronotum.

I've only been to see Variable Damselflies three times and was struck by the variablity of the males - in particular the antehumeral stripes.

The only other male damselfly that you might encounter in Hampshire that is predominantly blue is White-legged Damselfly which should not be confused because of its orangey pterostigma and two complete black lines on the side of the thorax.

Female Blue Damselflies

are most likely to be seen attached to a male so it can take longer to see enough individuals to gain experience in identifying them. There are two colour forms for females of the species. The next image shows the blue forms for Southerm, Azure, Variable and Common Blue damselflies (mainly because I haven't got any decent images of the other forms!). Thanks to Pete Ridout for his female Variable image.

As for the male, female Common Blue Damselflies have broad antehumeral (shoulder) stripes and lack the 'Coenagrion spur' ; they also have a triangular (or pyramidal) dark pattern on S8; there is an obvious spine under S8 which is not present in the other blues. The two images below of an immature female show (a) the broad antehumeral stripe and lack of 'Coenagrion spur' and (b) the spine under S8 and the triangular pattern on S8.

Warning: A spine under S8 is also present in female Blue-tailed Damselflies so should not be used as a sole feature to determine the species.

Southern, Azure and Variable are less easy to separate. They all have the Coenagrion spur and a thistle shape on S2 (the blue form Variable has a 'mercury' shape but as you can see from the image above it's not particularly obvious) and the dark forms look identical (I'll get some images one day!). If there is a pale bar between the post-ocular spots then it is most likely either a Southern or a Variable - but occasionally female Azures have this feature. However, this pale bar can be difficult to see in the field and may not always be present in female Variables or Southerns. See Exceptions

The key feature in identifying female (coenagrion) blues is the shape of the pronotum and in particular the rear edge. Looking at the picture below the Azure has a gently wavy three lobed rear edge with a clear pale margin; the Southern has a small lobe in the middle of a rear edge that is straighter than in Azure; the Variable has a strongly tri-lobed rear edge with the central lobe more prominent than in Azure. (You can also the pale bar between the post-ocular spots on Southern and Variable in this photo although it can be absent in both species and Azure can occasionally have a bar)